The extraction of various analytes from solid matrix samples using a fluid under elevated temperatures and pressures sufficient to cause the fluid to be in a supercritical condition is well known and has been in use for many years. Carbon dioxide, for example, is a commonly employed material for supercritical analyte extraction. The carbon dioxide will be held in a container or cell which is raised to a temperature and pressure which causes the carbon dioxide to operate as a supercritical fluid. While in the supercritical conditions, the fluid is forced through a porous sample to cause extraction of analytes from the sample. A wide range of samples and analytes are amenable to such supercritical extraction techniques.
It also has been found that the addition of a solvent to a supercritical fluid, in relatively low percentages, for example, 10% or less, will enhance the supercritical extraction process. While supercritical fluid extraction, with solvent augmentation, enhances the supercritical fluid extraction result, the temperatures and pressures at which the fluid is maintained in supercritical condition are greater than would be optimum for a pure solvent extraction.
Accordingly, it has been recently discovered that a highly effective solvent extraction process for the extraction of organic analytes from a solid matrix sample can be accomplished by maintaining an organic analyte in contact with a non-aqueous organic solvent system in an extraction cell under temperatures of pressure below supercritical conditions. This process is described in detail in commonly owned, parent U.S. patent application Ser. No. 08/259,667, filed Jun. 14, 1994, and entitled "Accelerated Solvent Extraction System," which application is incorporated herein by reference in its entirety.
While solvent extraction at elevated temperatures below supercritical conditions has been found to be highly advantageous, it further is highly desirable to provide a method and apparatus for automatic operation of such a solvent extraction process. Moreover, for applications in which supercritical fluid extraction has advantages over a solvent extraction process, it is desirable to have an apparatus and method for automating the supercritical fluid extraction process.
There are commercially available apparatus for automating the supercritical fluid extraction process, but such systems have had disadvantages in the cells employed, their sealing schemes and the physical manipulation of cells and collection vials. Such apparatus do broadly include, however, cell storage trays, oven assemblies, extraction fluid communication assemblies and devices for moving the respective components in an automated sequence.
Accordingly, it is an object of the present invention to provide a method and apparatus which is suitable for automated analyte extraction using a solvent extraction process or a supercritical fluid extraction process which employs enhanced component handling and cell sealing structures that increase operational safety and reduce contamination potential.
Another object of the present invention is to provide an automated analyte extraction apparatus and method which allows high temperature and high pressure extractions to be automatically accomplished rapidly and with minimal technician supervision.
A further object of the present invention is to provide an automated analyte extraction system which is durable, low in cost, easy to maintain, will accommodate samples of various size, and is suitable for single or multiple cycle extractions.